ACQUISITIONS (Narrative) (Details) € in Millions, CAD in Millions, $ in Millions								3 Months Ended		9 Months Ended
	Mar. 01, 2017 USD ($) building Center item mi	Oct. 03, 2016 USD ($) ft² item MW	Apr. 01, 2016 USD ($) ft² Center	Jan. 15, 2016 CAD building item mi	Jan. 15, 2016 USD ($) building item mi	Dec. 31, 2015 EUR (€) ft²	Dec. 31, 2015 USD ($) ft²	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Mar. 31, 2017 USD ($) item	Mar. 31, 2016 USD ($)
Business Acquisition [Line Items]
Number of business combinations completed since inception | item										40
Cash paid for acquisitions										$ 1,426.8	$ 417.0
Acquisition related costs								$ 8.4	$ 14.2	17.6	$ 17.5
Electric Lightwave [Member]
Business Acquisition [Line Items]
Acquisition date	Mar. 01, 2017
Number of metropolitan markets | item	35
Business acquisition purchase price	$ 1,426.7
Purchase price held in escrow	14.0
Remaining cash consideration to be paid	$ 2.2
Number of on-net buildings connected | building	3,100
Number of data centers | Center	100
Santa Clara Data Center [Member]
Business Acquisition [Line Items]
Acquisition date		Oct. 03, 2016
Business acquisition purchase price		$ 11.3
Remaining cash consideration to be paid		$ 10.2
Number of quarterly payments | item		10
Amount of quarterly payments		$ 1.3
Cash paid for acquisitions		$ 2.3
Acquired facility size (in square feet) | ft²		26,900
Acquired megawatts of critical power | MW		3
Clearview [Member]
Business Acquisition [Line Items]
Acquisition date			Apr. 01, 2016
Business acquisition purchase price			$ 18.3
Number of data centers | Center			2
Cash paid for acquisitions			$ 18.3
Acquired facility size (in square feet) | ft²			30,000
Business acquisition, percentage of voting interests acquired			100.00%
Allstream, Inc. [Member]
Business Acquisition [Line Items]
Acquisition date				Jan. 15, 2016	Jan. 15, 2016
Number of metropolitan markets | item				5	5
Business acquisition purchase price					$ 297.6
Acquired route miles added to fiber network | mi				18,000	18,000
Number of on-net buildings connected | building				3,300	3,300
Cash paid for acquisitions				CAD 422.9	$ 297.6
Business acquisition, percentage of voting interests acquired					100.00%
Working capital and other liabilities assumed in the acquisition					$ 29.6
Other post retirement benefits plan liability assumed					$ 8.3			$ 12.9		$ 12.9
Viatel [Member]
Business Acquisition [Line Items]
Business acquisition purchase price							$ 101.2
Cash paid for acquisitions						€ 92.9	101.2
Business acquisition, percentage of voting interests acquired								100.00%		100.00%
Refund of escrow reflected as a cash inflow from investing activities										$ 1.5
Dallas Data Center [Member]
Business Acquisition [Line Items]
Business acquisition purchase price							16.6
Cash paid for acquisitions							$ 16.6
Acquired area in square feet | ft²						36,000	36,000
Long-Haul Fiber [Member] | Electric Lightwave [Member]
Business Acquisition [Line Items]
Acquired route miles added to fiber network | mi	8,100
Long-Haul Fiber [Member] | Allstream, Inc. [Member]
Business Acquisition [Line Items]
Acquired route miles added to fiber network | mi				12,500	12,500
Metro Fiber [Member] | Electric Lightwave [Member]
Business Acquisition [Line Items]
Acquired route miles added to fiber network | mi	4,000
Metro Fiber [Member] | Allstream, Inc. [Member]
Business Acquisition [Line Items]
Acquired route miles added to fiber network | mi				5,500	5,500